An electrophotographic printer known in the art has developing devices detachably mounted therein. Each developing device includes a developing-device frame, and a developing roller and a supply roller supported in the developing-device frame.
One such developing device that has been proposed is a developer cartridge that includes a cartridge frame, a developing roller rotatably supported in the cartridge frame, and a supply roller rotatably supported in the cartridge frame while confronting and contacting the developing roller. The developer cartridge also includes grooves formed one each in the left and right side walls of the cartridge frame for receiving ends of a rotational shaft provided in the developing roller, and through-holes formed in the left and right side walls for inserting ends of a rotational shaft provided in the supply roller. The groove and through-hole formed in the left side wall are in communication.